1. Field of the Invention
This invention relates generally to semiconductor photodetectors and, more specifically, to an angle cavity resonant semiconductor photodetector that is able to generate an electrical output for a specific range of light using a waveguide and multiple reflectors to create a resonance of light within the photodetector.
2. Discussion of the Related Art
High frequency, wide bandwidth photodetectors, such as PIN photodiodes, that are used in a variety of systems for the transfer of light as a primary means of transferring information are known in the art. These systems are especially needed for high-speed communication systems, such as automatic teller machines, computer network systems, and multimedia applications.
Photodetectors are used to convert optical energy into electrical energy. A photodiode is typically used for high-speed applications. In high-speed applications, the speed and the responsivity of the photodetector are critical. Although fiber optic cable can transmit at speeds of greater than 100 GHz, current technology photodetectors are limited to 45-60 GHz bandwidths. With the current explosion of multimedia technologies and applications, such as the Internet, the telecommunications industry will require higher bandwidth systems such as optical systems with high speed phododiodes.
In the typical photodiode, an active semiconductor material generates an electrical current by the photogenerated electrons within the active material. Responsivity and speed are two variables that are often used to determine the performance of photodetectors. Responsivity is the measure of the effectiveness of a device in converting incident light to an output current. Speed is the measure of how quickly an output of the device changes in response to a change in the input to the device. For a photodiode to be effective in high-speed communication applications, it must have both a high responsivity and a high speed. Current high speed photodiodes typically have a responsivity of 0.2-0.4 amps/watt and a top end speed of 45-60 GHz. To increase the responsivity of a photodiode, the thickness of the active area is often increased so as to increase the quantum efficiency, thus creating more output current. This creates a problem, however, because a thicker active area increases the transit time, which decreases the speed.
Current high speed photodiode design must incorporate a tradeoff between quantum efficiency and bandwidth.
Most communication applications that involve photodiodes also require an optical coupling device for guiding the light to the photodiode active area. Since the requirements of the optical coupling device are to deliver the incident light to a relatively small area, typically there are a minimum number of components and materials that are required to carry out this task. Due to the difference of materials and the number of optical components that are used in the optical coupling device, there tends to be a high optical loss in the coupling device that degrades the overall performance of the photodiode.
State of the art optical communication systems have carriers of very high frequency that require the use of high-speed, high-responsivity photodetectors. As the demand for more information increases, so will the demand that communication systems be able to transmit more information, which will in turn require high-speed, high-responsivity photodetectors. The known photodetectors for high frequency applications are limited by having a low responsivity and a limited high-end frequency response. It has been recognized that the effectiveness of a communications system could be increased by providing a photodetector that employs multiple reflections between a waveguide and reflectors to produce a high responsivity and high-speed photodetector.
It is an object of the present invention to provide a resonant photodetector that provides for an increased responsivity and speed, as well as providing other improvements, over the known photodetectors, to improve the performance of the communication process.
In accordance with the teachings of the present invention, an angle cavity resonant photodetector assembly is disclosed that utilizes multiple reflections within a photodetector to convert an optical signal to a corresponding electrical signal output. The angle cavity resonant photodetector assembly includes a plurality of semiconductor layers that combine to define a waveguide, a photodetector, and supporting structure and circuitry.
The waveguide provides a path to direct light to the photodetector from a light source. The waveguide includes a first end that is positioned to receive light from the light source, and reduce the number of optical components required to couple the light to the photodetector. The waveguide further includes cladding layers that refract the light propagating through the waveguide towards the photodetector to limit the amount of light that escapes from the waveguide.
The photodetector includes a plurality of semiconductor layers aligned at an angle relative to the propagation direction of the light traveling through the waveguide. The photodetector semiconductor layers include first and second reflectors opposite each other for providing multiple reflections of the light propagating through the photodetector active area. This use of multiple reflections within the photodetector increases the quantum efficiency and allows for a smaller active area to be used in the photodetector while retaining or increasing the efficiency of operation.
Additional objects, advantages and features of the present invention will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings.